Intracellular bacteria are the leading cause of death in the world, especially in developing countries and among immunocompromised individuals. The emergence of multi-drug resistant pathogens has increased the difficulty of controlling several of these infectious diseases such as tuberculosis. MHC class I restricted CD8+ T-cells play a central role in the control of intracellular bacterial infections. Most information about CD8 function concerns their ability to respond to antigens presented by the MHC class la molecules which include human HLA-A, B and C. The majority of genes in the MHC class I locus encode MHC class lb molecules yet information on class lb gene regulation, expression and function is quite limited. This proposal will examine the role of class lb molecules in antigen presentation, T-cell development, and immune response to pathogenic bacteria. Studies will focus on 112-M3, the best characterized MHC class lb molecule in the mouse. M3 has unique specificity for N-formylated peptides. Because prokaryotes initiate protein synthesis with N-formyl methionine, the peptide-binding specificity of M3 makes it especially well suited for presenting these unique bacterial epitopes to T cells. This proposal seeks to identify the M3-binding peptides from pathogenic intracellular bacteria in order to design a peptide-based cytolytic T-cell vaccine. Efficacy of protection will be assessed using in vivo infectious disease models. The highly specialized function of M3 suggests that an as yet unidentified human homolog exists. She will attempt to clone the human M3 equivalent and characterize its antigen-binding motif. This will allow screening and design of immunogenic peptide vaccines for human M3-restricted T-cell responses. A peptide vaccine targeted for a class lb molecule has the clear advantage that a single peptide may work in all recipients, because class lb molecules are much less polymorphic than class la molecules. An important aspect of intracellular microbial pathogenesis is the mode of interaction between pathogen and host cell structures. To facilitate investigation of M3-restricted bacterial responses, she will analyze the molecular and cellular control of M3 transcription and protein trafficking. MHC class la molecules also play an important role in shaping the T-cell repertoire. Little is known about the development and thymic selection of class lb restricted T-cells. She will generate T-cell receptor transgenic mice specific for an M3-restricted ligand to study the role of class lb molecules in thymic selection. The ability of M3 to bind mitochondrial self-peptides may also make this a useful model for studying the mechanism of infection-induced autoimmunity.